This invention relates to a burn-in module having a heat exchanger for control of the heat generated by the power applied to a device under test (DUT).
Integrated circuits (ICs), after manufacture and prior to use in a computer system, undergo a variety of tests to ensure that they are defect free and will perform as intended. One of the tests conducted is known as burn-in.
Test systems for component testing are well know; for example, semi-conductor life tests in burn-in chambers are common. The process of burning-in typically consists of applying a load to the components being tested at elevated temperatures. This allows for identification of weak or faulty components and thus procludes their ultimate use, such as in a computer system.
In addition to burn-in ovens or hot air ovens, other technologies used for this purpose are open loop conduction heating, such as hot plates and thermal probes and liquid bath systems.
The burn-in ovens are by far the most prevalent test device and method used. Second in importance are the liquid burn-in bath methods.
In order to apply a load to the components under test, driver electronics, which must be isolated from the hot thermal environment of the high temperature oven or liquid bath, are used. This means that the driver electronics must be some distance from the devices under test (DUTs) which compromises frequency limits. Further, DUT trays must be constructed with an expensive high temperature material which adds to the costs of the testing procedure. The burn-in ovens, or forced air systems, typically have plus or minus 3.degree. C. gradients throughout the chamber as required by MIL-STD-883. However, device heat dissipation makes determining the actual case temperatures (and therefore, junction temperatures) very difficult. Materials used in the chamber must be rated at the highest operating temperature, i.e. sockets, capacitors, resistors, connectors and PC board material. Semi-conductors cannot be used on the PC board above 75.degree. C. because of their unreliability at these temperatures. High frequency applications (approximately 5 mHz) require the use of multi-layer polyimide, PCB's, mother boards, daughter boards and extender boards. High pin count devices require very high I/O's through chamber walls or a compromise must be made. Further, clock cards outside the chamber driving relatively long distances (typically as long as 30 inches) compromise the high frequency operation. In liquid bath systems, the problems are the same as in the burn-in ovens. Further, they are more expensive to operate, more inconvenient to operate and clock circuits cannot be put in the bath.
Briefly, some of the common problems with current technology is that the driver electronics are remote from the DUTs. This affects signal quality, the maximum signal frequency that can be used and results in signal skew, cross talk and overshoot. The I/O through the oven walls is not especially suitable for high pin count VLSI components and there is a practical limit to the number of I/O's and the possibility of impairment of signal quality. Perhaps the most severe problem is that there are temperature variations throughout the oven due to flow dynamics and one is never really sure of the actual DUT junction temperature. Further, the large monolithic ovens are not amenable to small lot burn-in, independent temperature cycling or independent DUT cool down under bias.
My prior inventions, see U.S. Pat. Nos. 5,164,661 and 5,126,656, comprised a thermal control system and a tower for burn-in of DUTs which accurately and independently controlled the device case temperature of each DUT with close-loop conductive heating and further included over temperature protection, under temperature protection and junction temperature correction. Using a close-loop method of conductive heating for each DUT, the prior inventions could heat the device case temperature to say 200.degree. C. at an accuracy of less than plus or minus 2.degree. C. The inventions used closed-loop sensors that read temperatures directly from the device case assuring that the DUT at each DUT position reached the desired temperature. A conductive module which included a heater and a sensor engaged the DUT. Therefore, a separate heat source serviced each position. Thermal control for each position was via a dedicated microprocessor with the processor set up in turn by a computer. With individual control, each position could be heated to different temperatures over different time intervals. Also, the sensor which read the temperature of the DUT was isolated from the heater which contacted the DUT. Therefore, the temperature reading was not influenced by the temperature of the heater. Further, the sensor and heater were individually suspended whereby uniform engagement with the DUT was ensured.
The system was preferably embodied in a tower-like structure where each position was located on the outer surface of the structure. The conductive module was secured to the outer surface of the tower, its heater and sensor extending outwardly. The DUT socket releasably engaged the conductive module at the DUT position. Mother boards containing the DUT clock card with driver electronics were arrayed vertically in the tower in a wall-like configuration and communicated with lower horizontally-fixed backplanes secured in the tower. These backplanes distributed the DC voltages to the mother boards which in turn distributed the load to the DUT's. Thermal control boards communicated with upper backplanes which backplanes were secured horizontally in the tower. These boards controlled the DUT device case temperature. The control board communicated with a microprocessor via the upper backplane.
The conductive modules were secured to the tower and passed through the mother board. The conductive modules were computer controlled by the thermal control boards. The DUT sockets frictionally engaged the mother board and electrically communicated therewith. The DUT contacted a sensor on the conductive module. Because the driver electronics were placed close to the DUT, the system provided signal quality greater than 40 mHz.
My prior inventions overcame the significant prior art problems as discussed above. However, as the DUT's being tested become more sophisticated and greater demands were placed on the testing of these components, it was found that with my prior system the power loads were such that the heat being generated could not be easily dissipated while maintaining the precise temperature control desired for testing. Also, it was discovered that there was a need for a much smaller system embodying the temperature control concept of my prior inventions and more specifically, a system for a single DUT, such as a portable system with a single DUT.
In the present invention, structural and functional changes have been made to my prior system to provide for a heat exchange fluid to be used in combination with a thermoconductive assembly, referred to in my patents as a conductive module. In a preferred embodiment, the heat exchange system maintains the thermoconductive assembly at a desired temperature while the temperature control of the DUT functions based on the DUT temperature sensor and the temperature sensor in the heating block.
Broadly the invention comprises a system for temperature control of a thermoconductive assembly used in the burn-in of a DUT. In a preferred embodiment, the heat exchange unit functions independently of the DUT temperature sensor which is received within the heat exchange device and the heating block temperature sensor as described in my patents.
In a preferred embodiment of the invention, the heat exchange fluid is used to remove heat from the thermoconductive assembly.
In an alternative embodiment of the invention, the heat exchanger functions in combination with the DUT temperature sensor and the heating block temperature sensor to control both the temperature of the thermoconductive assembly and the DUT.